The invention relates to a metal vapor laser discharge system and, more particularly, to a laser system including a cataphoresis type metal vapor laser.
The metal vapor laser is known as a laser developing a mixing discharge in a discharge tube filled with helium (He) gas and metal vapor of cadmium Cd, for example, as a medium. The metal vapor laser now commercially available is roughly classified into three types: helium and cadmium combination, helium and celenium combination, and helium and iodine combination. Other known metal vapor lasers now in the experimental and studying stage are helium and zinc, helium and tellurium, helium and mercury, helium and arsenic, helium and tin, and the like.
From a structural viewpoint, the metal vapor laser is categorized into an oven laser, hollow cathode laser, and a cataphoresis laser. The former two lasers are not used at present for various reasons and only the latter cataphoresis laser is practically used.
The output characteristic of the cataphoresis type laser having maturely been studied depends on the helium pressure in the laser tube, the concentration of metal vapor, i.e. the metal vapor pressure, and current density, i.e. the discharge current in the laser tube. In order to obtain a stable and maximum laser output, it is necessary to optimize these factors. However, such an optimization was difficult in the conventional laser system. For this, the conventional laser is unstable in output and short in life time. In laser oscillation, the metal vapor moves due to a cataphoresis effect and cools down near the cathode electrode to be condensed onto the inner surface of the laser discharge tube around the electrode. The result is reduction of the concentration of the metal evaporation in the laser discharge tube. During the laser oscillation, helium gas is diffused along the inner surface of the laser discharge tube and the metal vapor is condensed onto the inner surface of the tube. At this time, helium atoms are absorbed into the metal, with the result that the helium pressure is reduced.
Several attempts have been made to overcome such problems but these attempts have been unsuccessful.